The present invention relates to a method for welding a weld-on element, which has a weld-on end and a functional region arranged at a distance from the latter, onto a component, for example onto a vehicle panel.
Weld-on elements can be butt-welded onto components, for example metal panels, for example by what is known as arc welding. The function region of the weld-on elements projects from the components and may therefore hold various structural parts or components. In motor vehicle construction, for example, the weld-on elements may be placed with their weld-on end flush against a body panel or the like, welded to it, and be configured at their functional region so as to afford many different possibilities for holding various structural parts or components. The functional portion of each weld-on element is, in this case, variably designed so as to be adapted to the component to be held. For example, cable harnesses individual cables, lines, hoses and trim. The functional region may be configured in many different ways.
The arc welding method employed may be what is known as the lift-ignition welding method, as described for example in DE 199 25 628 A1.
Also known is the WELDFAST® welding method, in which weld-on elements, that is to say WELDFAST® holders as they are known commercially, are welded to a panel by arc welding. The WELDFAST® holders have the weld-on end and the functional region. However, it must be considered a disadvantage of the WELDFAST® holders that they have an elongated configuration at their weld-on ends, so as to form virtually a weld-on edge of a long extent. A specially configured welding appliance is required to reliably weld the weld-on elements to a panel. Welding defects may cause the welded-on weld-on element to fail. Welding parameters vary considerably on account of the elongated welding edge, thus making low-cost production difficult, since the welding parameters would always have to be continuously established and checked. The use of inert gas, intended for protecting the surrounding welding region from oxidation, also has the effect of increasing costs. For this purpose, a welding apparatus adapted to the WELDFAST® method has an inert-gas cover, which restricts free space.
In spite of the arc-stabilizing effect of argon as an inert gas, it has been observed that the arc is not always reproducibly stable, which has led to undesired instances of the panel being welded through or pierced. For example, it has been observed on weld-on elements with an elongated welding edge that arcs break away from certain portions of the welding edge but are maintained at other portions. Arcs pierce isolated points along the elongated area resulting in a weld of poor quality, which therefore has to be rejected. Poor or defective welds produced by arc welding methods, for example on the basis of the WELDFAST® system, can however only be spotted with great difficulty by means of automatic defect detection systems. Therefore, these welded connections are checked by manual visual inspections, and repaired by manual reworking, for example by applying welding or soldering filler to the location of the defect. This manual check with the additional requirement for manual repair is very cost-intensive.
Such components, or vehicle panels, to which the weld-on element can be welded, have a coating or a lubricant coating, applied for forming purposes. The lubricant layer is even more random if the vehicle panel has been in storage for a relatively long time because the lubricant coating is removed in some places due to gravity or for other reasons. For example, it is known to use drawing oil as a lubricant, sometimes leading to rapid drying out of the vehicle panels. DE 199 25 628 A1 proposes removing the lubricant coating before the actual welding process, by producing a cleaning current before the actual welding current, the cleaning current flowing via the weld-on element. This would form a lubricant-free welding zone. However, vehicle panels known as “dry” panels, which do not have a lubricant coating, are also increasingly being used.
Arcing occurs when the weld-elements have an elongated curved weld-on end. The arcs are unstable and break away from the panel and produce a weld of poor quality.